The present invention relates to power steering systems and pertains particularly to power steering for an electrically powered vehicle.
Vehicles such as lift trucks and the like used inside warehouses and the like are normally electrically powered because of ventilation problems associated with internal combustion engines. Such vehicles can be quite large and handle quite heavy loads. For this reason it is quite often necessary to have power steering on such vehicles.
Power steering systems for such vehicles are frequently hydraulically powered with fluid supplied by a pump driven by an electrical motor. The source of the steering fluid may also be the same source as that supplied for the tilt and lift cylinders of the lift assembly. Because of the infrequent use of these cylinders and because of the low volume of fluid required for the steering system, the system is normally constructed to cut off the electric motor when fluid is not required by one of the systems. This is done in an effort to save energy required for a constantly running motor.
On the other hand, the steering of such vehicles requires frequent correction of the steering and thus very frequent small supplies of fluid from the system. For this reason, as soon as the steering system is activated, the electric motor is immediately started. This constant starting and stopping of the electric motor also constitutes a considerable waste of electrical power and also results in severe wear and tear on the electric motor and system.